(1) Field of the Invention
The present invention is an improvement of an electron microscope with the features which are known from the publication of W. Telieps and E. Bauer, Ultramicroscopy 17 (1985) p. 57.
(2) Description of the Prior Art
In the identified, known electron microscope an electron beam supplied by an electron source is accelerated to an energy of 15 to 20 keV, deflected by a magnetic field and focused by means of an electron lens in the rear focal plane of a cathode lens. In the electric field of the cathode lens the electron beam is decelerated, so that it impinges on a sample surface to be investigated approximately as a parallel beam with low energy, which is adjustable to values from a few up to some 100 electron volts. The electrons elastically reflected from the atoms on the sample surface are accelerated again through the field of the cathode lens to the primary energy; at the same time they interfere with each other because of their wave nature, so that a diffraction pattern (LEED=low energy electron diffraction) results in the rear focal plane of the cathode lens, which represents the lattice arrangement of the surface atoms. In the magnetic field the returning reflected electron beam is separated from the incident primary beam. By means of following electron optics either the enlarged diffraction pattern can be made visible on a display screen or else the sample surface itself, very greatly enlarged. In the latter case the electrons from a single LEED reflection are selected, so that the image resulting on the display screen reproduces the local distribution of the relevant crystal structure.